Industrial refrigerator and its components Refrigeration machines and installations: device and principle of operation

An ordinary person, as a rule, does not need to understand the principle of operation of a refrigeration machine; the result is important for him. The result of the operation of the refrigeration unit is: chilled products - from frozen vegetables to meat and dairy products, or, for example, chilled air, if we are talking about split systems.

Another thing is when the refrigeration machines fail and a specialist call is required to repair the refrigeration units. In this case, it would not be bad to understand the principle of operation of such units. At least in order to understand the need to replace or repair a component of the refrigeration machine.

The main purpose of a refrigeration plant is to take heat from a cooled body and transfer this heat or energy to another object or body. To understand the process, it is necessary to understand a simple thing - if we heat or compress a body, then we impart energy (or heat) to this body, while cooling and expanding, we take away energy. This is the basic principle on which heat transfer is built.

In a refrigeration machine, refrigerants are used to transfer heat - the working substances of a refrigeration machine, which, when boiling and in the process of isothermal expansion, take heat from the object being cooled and then, after compression, transfer it to the cooling medium due to condensation.

The refrigeration compressor 1 sucks off the gaseous refrigerant - freon from the evaporators 3, compresses it and pumps it into the condenser 2. In the condenser 2, the freon condenses and passes into a liquid state. From the condenser 2, the liquid refrigerant enters the receiver 4, where it accumulates. The receiver is equipped with shut-off valves 19 at the inlet and outlet. From the receiver, the refrigerant enters the filter-drier 9, where the remaining moisture, impurities and contaminants are removed, then it passes through the sight glass with a humidity indicator 12, the solenoid valve 7 and is throttled by the thermostatic valve 17 into the evaporator 3.

In the evaporator, the refrigerant boils, taking heat from the object to be cooled. The refrigerant vapors from the evaporator through the filter on the suction line 11, where they are cleaned of contaminants, and the liquid separator 5 enter the compressor 1. Then the operation cycle of the refrigeration unit is repeated.

Liquid separator 5 prevents liquid refrigerant from entering the compressor. To ensure guaranteed oil return to the compressor crankcase, an oil separator 6 is installed at the compressor outlet. In this case, the oil enters the compressor through the shut-off valve 24, filter 10 and sight glass 13 along the return line.

Vibration isolators 25, 26 on the suction and discharge lines dampen vibrations during compressor operation and prevent their propagation along the refrigeration circuit.

The compressor is equipped with a crankcase heater 21 and two shut-off valves 20. The crankcase heater 21 evaporates the refrigerant from the oil, preventing the refrigerant from condensing in the compressor crankcase during its standstill and maintaining the set oil temperature.

Refrigeration is the process by which the room temperature is lowered below the outdoor temperature.

Air conditioning - this is the regulation of temperature and humidity in the room with the simultaneous implementation of air filtration, circulation and its partial replacement in the room.

Ventilation - it is the circulation and replacement of air in a room without changing its temperature. With the exception of special processes such as freezing fish, air is usually used as an intermediate heat transfer medium. Therefore, for the implementation of refrigeration, air conditioning and ventilation, fans and air ducts are used. The three processes mentioned above are closely interconnected and together provide a given microclimate for people, machines and cargo.

To reduce the temperature in cargo holds and in provisional storerooms during refrigeration, a cooling system is used, the operation of which is provided by a refrigeration machine. The selected heat is transferred to another body - a refrigerant at a low temperature. Air conditioning cooling is a similar process.

In the simplest schemes of refrigeration units, heat is transferred twice: first in the evaporator, where the refrigerant, which has a low temperature, takes heat from the cooled medium and reduces its temperature, then in the condenser, where the refrigerant is cooled, giving off heat to air or water. In the most common schemes of marine refrigeration plants (Fig. 1), a steam compression cycle is carried out. In the compressor, the vapor pressure of the refrigerant rises and its temperature rises accordingly.

Rice. 1. Scheme of a steam compressor refrigeration unit: 1 - evaporator; 2 - thermosensitive balloon; 3 - compressor; 4 - oil separator; 5 - capacitor; 6 - dryer; 7 - pipeline for oil; 8 - control valve; 9 - thermostatic valve.

This hot, pressurized steam is injected into the condenser, where, depending on the application conditions of the plant, the steam is cooled with air or water. Due to the fact that this process is carried out at elevated pressure, the steam is completely condensed. The liquid refrigerant is piped to a control valve which controls the liquid refrigerant supply to the evaporator where the pressure is kept low. The air from the refrigerated room or the conditioned air passes through the evaporator, causes the liquid refrigerant to boil, and itself, giving off heat, is cooled. The refrigerant supply to the evaporator must be adjusted so that all the liquid refrigerant in the evaporator is boiled off and the vapor is slightly superheated before it re-enters the compressor at low pressure for subsequent compression. Thus, the heat that has been transferred from the air to the evaporator is carried by the refrigerant through the system until it reaches the condenser, where it is transferred to the outside air or water. In installations where an air-cooled condenser is used, such as a small provisional refrigeration unit, ventilation must be provided to remove the heat generated in the condenser. For this purpose, water-cooled condensers are pumped with fresh or sea water. Fresh water is used in cases where other mechanisms of the engine room are cooled with fresh water, which is then cooled by sea water in a centralized water cooler. In this case, due to the higher temperature of the water cooling the condenser, the temperature of the water leaving the condenser will be higher than when the condenser is cooled directly by sea water.

Refrigerants and coolants. Cooling working fluids are divided mainly into primary - refrigerants and secondary - coolants.

The refrigerant under the influence of the compressor circulates through the condenser and evaporative system. The refrigerant must have certain properties that meet the requirements, such as boiling at low temperature and overpressure and condensing at a temperature close to sea water temperature and moderate pressure. The refrigerant must also be non-toxic, explosion-proof, non-flammable, non-corrosive. Some refrigerants have a low critical temperature, i.e. a temperature above which the refrigerant vapor does not condense. This is one of the disadvantages of refrigerants, in particular carbon dioxide, which has been used on ships for many years. Due to the low critical temperature of carbon dioxide, the operation of ships with carbon dioxide refrigeration plants in latitudes with high seawater temperatures was significantly hampered, and because of this, additional cooling condenser systems had to be used. In addition, the disadvantages of carbon dioxide include a very high pressure at which the system operates, which in turn leads to an increase in the mass of the machine as a whole. After carbon dioxide, methyl chloride and ammonia were widely used as refrigerants. Currently, methyl chloride is not used on ships due to its explosive nature. Ammonia still has some uses, but due to its high toxicity, special ventilation systems are required when using it. Modern refrigerants are fluorinated hydrocarbon compounds having various formulas, with the exception of the refrigerant R502 ( in accordance with the international standard (MS) HCO 817 - for the designation of refrigerants, the symbol of the refrigerant is used, which consists of the symbol R (refrigerant) and a defining number. In this regard, when translating, the designation of refrigerants R was introduced.), which is an azeotropic (fixed boiling point) mixture ( a specific mixture of different substances that has properties that are different from the properties of each substance separately.) refrigerants R22 and R115. These refrigerants are known as freons ( According to GOST 19212 - 73 (change 1), the name freon is established for freon), and each of them has a defining number.

The refrigerant R11 has a very low operating pressure, and to obtain a significant cooling effect, intensive circulation of the agent in the system is necessary. The advantage of this agent is especially evident when used in air conditioning installations, since relatively little power is required for air.

The first of the freons, after they were discovered and became available, freon R12 was widely used in practice. Its disadvantages include low (below atmospheric) boiling pressure, as a result of which, due to any leaks in the system, air and moisture are sucked into the system.

At present, the most common refrigerant is R22, which provides cooling at a sufficiently low temperature level at an excessive boiling pressure. This allows you to get some gain in the volume of the unit's compressor cylinders and other advantages. The volume described by the compressor piston operating on R22 freon is approximately 60% compared to the described volume of the compressor piston operating on R12 freon under the same conditions.

Approximately the same gain is obtained when using freon R502. In addition, due to the lower compressor discharge temperature, the likelihood of lube oil coking and failure of discharge valves is reduced.

All of these refrigerants are non-corrosive and can be used in hermetic and sealless compressors. To a lesser extent, the R502 refrigerant used in electric motors and compressors affects varnishes and plastic materials. At present, this promising refrigerant is still quite expensive and therefore has not been widely used.

Coolants are used in large air conditioning installations and in refrigeration plants that cool cargo. In this case, the refrigerant circulates through the evaporator, which is then sent to the room to be cooled. The refrigerant is used when the installation is large and branched, in order to eliminate the need to circulate in the system a large amount of expensive refrigerant, which has a very high penetrating power, i.e. it can penetrate through the slightest leaks, therefore it is very important to minimize the number of connections pipelines in the system. For air conditioning units, the usual coolant is fresh water, which may have the addition of a glycol solution.

The most common coolant in large refrigeration units is brine - an aqueous solution of calcium chloride, to which inhibitors are added to reduce corrosion.

At the dairy plant, a single-stage refrigeration system is used.

1 - compressor; 2 - capacitor; 3 - evaporators; 4 - receiver;

5 - liquid separator; 6 - oil separator; 7 - solenoid valve;

9 - filter-drier; 10 - filter; 11 - filter on the suction line; 12 - sight glass with humidity indicator; 13 - sight glass;

14 - high pressure switch; 15 - low pressure switch; 16 - emergency high and low pressure switch; 17 - thermostatic valve; 18 - oil pressure control relay; 19 - shut-off valve of the receiver; 20 - compressor shut-off valve; 21 - crankcase heater; 25, 26 - vibration isolators.

Figure 4 - Scheme of the refrigeration unit

The cooling process is based on the physical phenomenon of heat absorption during boiling (evaporation) of a liquid (liquid refrigerant). The compressor of the refrigeration machine is designed to suck gas from the evaporator and compress it, forcing it into the condenser. When compressing and heating refrigerant vapors, we give them energy (or heat), while cooling and expanding, we take away energy. This is the basic principle on which heat transfer occurs and the refrigeration plant operates. Refrigerants are used in refrigeration to transfer heat.

The refrigeration compressor (1) sucks the gaseous refrigerant from the evaporators (3), compresses it and pumps it into the condenser (2) (air or water). In the condenser (2), the refrigerant condenses and becomes liquid. From the condenser (2), the liquid refrigerant enters the receiver (4), where it accumulates. Also, the receiver is necessary to constantly maintain the required level of refrigerant. The receiver is equipped with shut-off valves (19) at the inlet and outlet. From the receiver, the refrigerant enters the filter-drier (9), where the remaining moisture, impurities and contaminants are removed, after that it passes through a sight glass with a humidity indicator (12), a solenoid valve (7) and is throttled by a thermostatic valve (17) into the evaporator ( 3).

The expansion valve is used to control the flow of refrigerant to the evaporator.

In the evaporator, the refrigerant boils, taking heat from the object to be cooled. The refrigerant vapors from the evaporator through the filter on the suction line (11), where they are cleaned from impurities, and the liquid separator (5) enter the compressor (1). Then the cycle of operation of the refrigeration machine is repeated.

The liquid separator (5) prevents liquid refrigerant from entering the compressor.

To ensure guaranteed oil return to the compressor crankcase, an oil separator (6) is installed at the compressor outlet. In this case, the oil through the shut-off valve (24), filter (10) and sight glass (13) through the oil return line enters the compressor.

Vibration isolators (25), (26) on the suction and discharge lines provide damping of vibrations during compressor operation and prevent their propagation along the refrigeration circuit.

The compressor is equipped with a crankcase heater (21) and two shut-off valves (20).

The crankcase heater (21) is necessary to evaporate the refrigerant from the oil, prevent the refrigerant from condensing in the compressor crankcase when it is stopped, and maintain the required oil temperature.

Chillers with semi-hermetic reciprocating compressors that use an oil pump in the lubrication system use an oil pressure switch (18). This relay is designed for emergency shutdown of the compressor in the event of a decrease in oil pressure in the lubrication system.

If the unit is installed outdoors, it must be additionally equipped with a hydraulic condensing pressure regulator to ensure stable operation in winter conditions and maintain the required condensing pressure in the cold season.

The high pressure switches (14) control the on/off of the condenser fans to maintain the required condensing pressure.

The low pressure switch (15) controls the on/off of the compressor.

The high and low pressure alarm switch (16) is designed for emergency shutdown of the compressor in case of low or high pressure.

Cooling of various objects - food, water, other liquids, air, technical gases, etc. to temperatures below ambient temperature occurs with the help of various types of refrigeration machines. The refrigeration machine, by and large, does not produce cold, it is only a kind of pump that transfers heat from less heated bodies to more heated ones. The cooling process is based on the constant repetition of the so-called. reverse thermodynamic or in other words refrigeration cycle. In the most common vapor-compression refrigeration cycle, heat transfer occurs during phase transformations of the refrigerant - its evaporation (boiling) and condensation due to the consumption of energy supplied from outside.

The main elements of the refrigeration machine, with the help of which its operating cycle is implemented, are:

• compressor - an element of the refrigeration cycle, providing an increase in the pressure of the refrigerant and its circulation in the circuit of the refrigeration machine;
• the throttling device (capillary tube, expansion valve) serves to regulate the amount of refrigerant entering the evaporator depending on the superheat on the evaporator.
• evaporator (cooler) - a heat exchanger in which the refrigerant boils (with heat absorption) and the cooling process itself;
• condenser - a heat exchanger in which, as a result of the phase transition of the refrigerant from a gaseous state to a liquid state, the removed heat is discharged into the environment.

In this case, it is necessary to have other auxiliary elements in the refrigeration machine, such as electromagnetic (solenoid) valves, instrumentation, sight glasses, filter driers, etc. All elements are connected to each other in a sealed internal circuit using pipelines with thermal insulation. The refrigeration circuit is filled with refrigerant in the required quantity. The main energy characteristic of a refrigeration machine is the coefficient of performance, which is determined by the ratio of the amount of heat removed from the cooled source to the energy consumed.

Chillers, depending on the principles of operation and the refrigerant used, are of several types. The most common vapor compression, steam jet, absorption, air and thermoelectric.

refrigerant

Refrigerant is the working substance of the refrigeration cycle, the main characteristic of which is a low boiling point. As refrigerants, various hydrocarbon compounds are most often used, which may contain atoms of chlorine, fluorine or bromine. Also, the refrigerant can be ammonia, carbon dioxide, propane, etc. Rarely, air is used as a refrigerant. In total, about a hundred types of refrigerants are known, but they are manufactured industrially and are widely used in refrigeration, cryogenic engineering, air conditioning and other industries, only about 40. These are R12, R22, R134A, R407C, R404A, R410A, R717, R507 and others. The main area of ​​application of refrigerants is the refrigeration and chemical industries. In addition, some freons are used as propellants in the manufacture of various aerosol products; foaming agents in the production of polyurethane and heat-insulating products; solvents; as well as substances that inhibit the combustion reaction, for fire extinguishing systems of various objects of increased danger - thermal and nuclear power plants, civilian ships, warships and submarines.

Expansion valve (TRV)

The thermostatic expansion valve (TRV) is one of the main components of refrigeration machines, and is known as the most common element for throttling and finely regulating the flow of refrigerant to the evaporator. The expansion valve uses a needle type valve adjacent to the poppet base as the refrigerant flow control valve. The amount and flow rate of the refrigerant is determined by the flow area of ​​the expansion valve and depends on the temperature at the outlet of the evaporator. When the temperature of the refrigerant at the outlet of the evaporator changes, the pressure inside this system changes. When the pressure changes, the flow area of ​​the expansion valve changes and, accordingly, the refrigerant flow changes.

The thermal system is filled at the factory with a precisely defined amount of the same refrigerant that is the working medium of this refrigeration machine. The task of the expansion valve is to throttle and regulate the refrigerant flow at the evaporator inlet in such a way that the cooling process takes place in it most efficiently. In this case, the refrigerant must completely go into a vapor state. This is necessary for the reliable operation of the compressor and the exclusion of its operation of the so-called. "wet" running (i.e. compressing the fluid). The thermal bulb is attached to the pipeline between the evaporator and the compressor, and at the attachment point it is necessary to ensure reliable thermal contact and thermal insulation from the effects of ambient temperature. Over the past 15-20 years, electronic expansion valves have become widespread in refrigeration technology. They differ in that they do not have a remote thermal system, and its role is played by a thermistor attached to the pipeline behind the evaporator, connected by a cable to a microprocessor controller, which in turn controls the electronic expansion valve and, in general, all the working processes of the refrigeration machine.

The solenoid valve is used for on-off control (“open-closed”) of the refrigerant supply to the evaporator of the refrigerating machine or for opening and closing certain sections of pipelines from an external signal. In the absence of power to the coil, the valve disc, under the influence of a special spring, keeps the solenoid valve closed. When power is applied, the core of the electromagnet, connected by a rod to the plate, overcomes the force of the spring, is drawn into the coil, thereby raising the plate and opening the flow area of ​​the valve for supplying refrigerant.

The sight glass in the refrigeration machine is designed to determine:

1. state of the refrigerant;
2. the presence of moisture in the refrigerant, which is determined by the color of the indicator.

The sight glass is usually mounted in the pipeline at the outlet of the storage receiver. Structurally, the sight glass is a metal hermetic case with a transparent glass window. If the chiller is operating through the window with liquid flowing through the window with individual bubbles of vaporous refrigerant, this may indicate insufficient charge or other malfunctions in its operation. A second sight glass can also be installed at the other end of the above pipeline, in close proximity to the flow controller, which can be a solenoid valve, an expansion valve or a capillary tube. The color of the indicator indicates the presence or absence of moisture in the refrigeration circuit.

The filter drier or zeolite cartridge is another important element of the refrigeration circuit. It is necessary to remove moisture and mechanical impurities from the refrigerant, thereby protecting the expansion valve from clogging. It is usually mounted with soldered or nipple connections directly into the pipeline between the condenser and the expansion valve (solenoid valve, capillary tube). Most often, it is structurally a piece of copper pipe with a diameter of 16 ... 30 and a length of 90 ... 170 mm, rolled up on both sides and with connecting pipes. Inside, two metal filter meshes are installed along the edges, between which a granular (1.5 ... 3.0 mm) adsorbent is located, usually a synthetic zeolite. This is the so-called. disposable filter drier, but there are reusable filter designs with a collapsible housing and threaded pipeline connections that require only an occasional replacement of the internal zeolite cartridge. Replacement of a one-time filter-drier or cartridge is necessary after each opening of the internal circuit of the refrigeration machine. There are unidirectional filters designed to work in "cold only" systems and bidirectional filters used in "heat-cold" units.

Receiver

Receiver - a sealed cylindrical storage tank of various capacities, made of steel sheet, and used to collect liquid refrigerant and its uniform supply to the flow regulator (TRV, capillary tube) and to the evaporator. There are receivers of both vertical and horizontal types. There are linear, drainage, circulation and protective receivers. The linear receiver is installed by means of solder joints in the pipeline between the condenser and the expansion valve and performs the following functions:

• ensures continuous and uninterrupted operation of the refrigeration machine under various thermal loads;
• is a hydraulic lock that prevents the ingress of refrigerant vapor into the expansion valve;
• performs the function of oil and air separator;
• frees the condenser tubes from liquid refrigerant.

Drainage receivers are used to collect and store the entire amount of charged refrigerant for the period of repair and service work associated with depressurization of the internal circuit of the refrigeration machine.

Circulation receivers are used in pump-circulation circuits for supplying liquid refrigerant to the evaporator to ensure continuous operation of the pump and are mounted in the pipeline after the evaporator at the point with the lowest elevation mark for free draining of liquid into it.

Protective receivers are designed for pumpless schemes for supplying freon to the evaporator; they are installed together with liquid separators in the suction pipeline between the evaporator and the compressor. They serve to protect the compressor from possible wet running.

A pressure regulator is an automatically controlled control valve used to reduce or maintain refrigerant pressure by changing the hydraulic resistance to the flow of liquid refrigerant passing through it. Structurally, it consists of three main elements: a control valve, its actuator and a measuring element. The actuator directly acts on the valve disc, changing or closing the flow area. The measuring element compares the current and set value of the refrigerant pressure and generates a control signal for the control valve actuator. In refrigeration, there are low pressure regulators, often called pressure switches. They control the boiling pressure in the evaporator and are installed in the suction pipe after the evaporator. High pressure regulators are called manocontrollers. They are most often used in air-cooled chillers to maintain the minimum required condensing pressure when the outside temperature drops during the transitional and cold seasons, thereby providing the so-called. winter regulation. The manocontroller is installed in the discharge pipeline between the compressor and the condenser.

In order to navigate when kitchen equipment fails, many housewives are forced to understand the principle of operation of many devices, such as an electric stove, microwave, refrigerator, and others. The main function of the cold store is to keep nutritious food fresh, so it must be constantly running, and the services of a repair specialist cannot be used instantly. Understanding how the refrigerator works will help save financial and time resources, and many malfunctions can be fixed by hand.

Refrigerator interior

Everyone knows how a refrigerator works, in simple words - this equipment freezes and cools a variety of products, allowing them to avoid spoilage for some time.

At the same time, not everyone knows certain features of this device: what the refrigerator consists of, where the cold comes from in the inner plane of the chamber, how it is created by the refrigerator, and why the device turns off from time to time.

To understand these issues, it is necessary to consider in detail the principle of operation of the refrigerator.. To begin with, we note that cold air masses do not arise by themselves: a decrease in air temperature is carried out inside the chamber during the operation of the unit.

This refrigeration equipment includes several main parts:

• coolant;
• evaporator;
• capacitor;
• compressor.

The compressor is a kind of heart of any refrigeration unit.. This element is responsible for the circulation of the refrigerant through a large number of special tubes, some of which are located behind the refrigerator. The remaining parts are hidden in the inside of the chamber under the panel.

During operation, the compressor, like any motor, is subjected to significant heat, so it needs some time to cool down. So that this unit does not lose its performance due to overheating, a relay is built into it that opens the electrical circuit at certain temperature indicators.

The tubes located on the outer surface of the refrigeration equipment are the condenser. It is designed to release heat energy to the outside. The compressor, pumping the refrigerant, sends it inside the condenser by means of high pressure. As a result, a substance with a gaseous structure (isobutane or freon) becomes liquid and begins to heat up. Excess heat is then dissipated in the room so that the cooling of the refrigerant occurs naturally. It is for this reason that it is forbidden to install heating devices near refrigerators.

The owners, who know about the principle of operation of the refrigerator, try to arrange for their "kitchen assistant" the most optimal conditions for cooling the condenser and compressor. This allows you to extend its service life..

To obtain cold in the inner chamber there is another part of the pipe system, into which the liquefied gaseous substance is sent after the condenser - it is called the evaporator. This element is separated from the condenser by a drying filter and a capillary. The principle of cooling inside the chamber:

• Once in the evaporator, freon begins to boil and expand, again transforming into a gas. In this case, thermal energy is absorbed.
• The tubes in the chamber cool not only the air masses of the unit, but also cool themselves.
• The refrigerant is then sent back to the compressor and the cycle repeats.

In order for nutritious foods not to freeze inside the refrigerator, a thermostat is built into the equipment. A special scale makes it possible to set the required degree of cooling, and after reaching the desired values, the equipment automatically turns off.

Single chamber and double chamber models

The air-cooling unit in each refrigerator has a general device principle. However, there are still differences in the functioning of different equipment. They are based on the characteristics of refrigerant movement in refrigerated cabinets with one or a pair of chambers.

The scheme, which was presented a little higher, is typical for single-chamber models. Regardless of the location of the evaporator, the principle of operation will be the same. However, if the freezer is located under or above the cooling compartment, then an additional compressor is required for stable and full-fledged operation of the refrigerator. For the freezer, the principle of operation will be the same.

The cooling compartment, in which the temperature does not drop below zero, starts only after the freezer has cooled down sufficiently and turned off. Just at this moment, the refrigerant from the freezer system is sent to the positive temperature chambers, and the evaporation / condensation cycle is already at a lower level, so it is impossible to say exactly how long the refrigeration equipment needs to work before automatic shutdown. It all depends on the setting of the thermostat and the volume of the freezer.

Quick freeze function

This function is typical for two-chamber refrigerators. In this mode, the refrigerator can work continuously for a long time. Fast freezing is intended for effective freezing of products in large volumes..

After activating the option, special LED indicators on the panel light up, indicating that the compressor is running. Here it is necessary to take into account the fact that the operation of the unit will not be stopped automatically, and too long operation of the refrigerator may adversely affect its condition.

After manual shutdown of the unit, the indicators will turn off by themselves and the compressor drive will turn off.

Modern refrigerators are equipped with a wide variety of functions. And today, housewives know about the existence of the automatic defrost function. Freeze-free and drip refrigeration systems have made human life much easier, but the principle of operation of the refrigerator has remained the same.